Abrading arrangement to abrade a surface of an item and method of use thereof

ABSTRACT

An abrasion arrangement is disclosed to abrade a surface of an item, the arrangement comprising a multiple axis robotic arm having at least five axes, an abrading cylinder mounted on the robotic arm and comprising abrasive means which comprise abrasive lamellae of an abrasive sheet, such as abrasive cloth, of which the front side has abrasive properties and which extend substantially radially from an elongated core and means for driving said core to rotate around a longitudinal axis of the core, and control means for controlling the operation of the robotic arm so to control e.g. the position of the abrading cylinder on said surface, the force with which the abrading cylinder is pressed towards said surface and the velocity with which the abrading cylinder is moved with respect to said surface.

The present invention relates to an arrangement comprising a robotic armcarrying abrasive means for abrading the surface of an item and methodof use of the arrangement.

BACKGROUND

Abrasion of the surface of items of a reasonable size by means of astationary abrading machine is well-known in the art from e.g. WO2004/098831. However, the abrasion of the surface of larger items, whereit is impractical to provide stationary abrasive means of dimensionssufficiently large is e.g. known to be provided by means of a roboticarm carrying abrasive means as disclosed in US 2002/0072297 for thesurface treatment of panels for aircrafts and from the Spanish companyEINA which in the magazine Wind Systems of March 2010 disclosed surfacegrinding of a wind turbine blade by means of a 8-axis robot handlinge.g. a sanding head having a plurality of abrasive disks arranged.

However, improvements of the means for abrading the surface of largeitems in order e.g. to remove irregularities and prepare the surface forpainting are requested and it is an object of the present invention toprovide such improvements.

BRIEF DESCRIPTION OF THE PRESENT INVENTION

The present invention relates to an abrasion arrangement to abrade asurface of an item, the arrangement comprising a multiple-axis roboticarm having at least five axes, an abrading cylinder mounted on therobotic arm and comprising abrasive means which comprise abrasivelamellae of an abrasive sheet, such as abrasive cloth, of which thefront side has abrasive properties and which extend substantiallyradially from an elongated core and means for driving said core torotate around a longitudinal axis of the core, and control means forcontrolling the operation of the robotic arm so as to control e.g. theposition of the abrading cylinder on said surface, the force with whichthe abrading cylinder is pressed towards said surface and the velocitywith which the abrading cylinder is moved with respect to said surface.

The abrading cylinder in itself is well known from e.g. from WO 01/76824and partly from the above-mentioned WO 2004/098831 and as well as from anumber of other documents with various embodiments. The type of abradingcylinders disclosed in WO 01/76824 is preferred in the presentinvention.

With the term velocity herein understood a vector, i.e. the speed aswell as the direction of movement. The cylinder is rotated so that thefront side of the abrasive lamellae is moved across the surface to beabraded. The tangential movement of the front side of the lamellae overthe surface to be abraded due to the rotation of the cylinder definesherein the abrading direction of the cylinder.

With the term robotic arm is herein understood a multiple-axis armhaving at least 5 degrees of freedom, i.e. that it is able to move theabrading cylinder across the surface of the item, towards and away fromsaid surface, to tilt the abrading cylinder in various planes and thatit is able to rotate the abrading cylinder about an axis substantiallynormal to the surface of the item, so that the abrading direction of thecylinder may be reversed by a 180° rotation. The robotic arm is at leasta 5-axis arm and most preferred a 6-axis arm, however robotic arms withhigher degrees of freedom could also be employed. With a robotic armhaving a degree of freedom of 5, 6 or even more, the arm with thecylinder becomes a more flexible abrading tool that can adjust better toa complex double curved surface of the item to be abraded and will beable to handle areas around edges more gentle.

An advantage obtained by employing the abrading cylinder as described isthat a more efficient abrasion of a surface may be obtained as comparedto the use of abrasive disks and the abrading cylinder is in itselfflexible to the shape of the surface and does not need to be perfectlyaligned with the surface to perform the abrading of the surfacesatisfactory. It also readily abrades surfaces of complex shapes such asdouble-curved surfaces. A drawback of the abrading cylinder is that itis only efficient when the relative movement of the surface and theabrading cylinder causes the surface to move in the opposite directionof the movement of the abrasive lamellae caused by the rotation of thecylinder, because the movement of the object in that case enhances themovement of the abrasive lamellae with respect to the surface, whereasrelative movement of the surface against the direction of the movementof the abrasive lamellae caused by the rotation of the cylinder weakensthe abrasive effect on the surface. Thus, the abrading cylinder isgenerally applied in machines as shown in the above-discussed WO2004/098831 with a uniform relative movement of the item with respect tothe abrading cylinder.

Furthermore, the abrading cylinder is not particularly suitable for usenear edges of items as the rotation of the cylinder may cause theabrasive lamellae to collide with the edge of the item in case the axisof rotation of the cylinder is not substantially perpendicular to theedge, if the abrading direction of the cylinder is towards the surfaceof the item and not towards the edge of the item. The abrasive lamellaewill collide with the edge which has a damaging and life-shorteningeffect on the lamellae as well a damaging effect on the edge of theitem. This may however be avoided by the present combination of anabrading cylinder and a robotic arm, which allow for advances control ofthe operational position of the cylinder. According to a preferredembodiment of the present invention, the control means are adapted tomove the abrading cylinder across said surface to alternate between

first movement in a direction substantially perpendicularly to thelongitudinal axis of the core and substantially in the same direction asan abrading direction of the rotated cylinder, the first movement beingcontinued until an edge of said surface is reached,

translating the cylinder substantially in a direction perpendicularly tothe direction of the first movement,

second movement in a direction substantially perpendicularly to thelongitudinal axis of the core and substantially against an abradingdirection of the rotated cylinder,

rotation of the cylinder half a turn to reverse the abrading directionthereof with respect to said surface, and

third movement in a direction substantially perpendicularly to thelongitudinal axis of the core and substantially in the same direction asan abrading direction of the rotated cylinder.

This working pattern of the abrasion arrangement provides for atime-efficient abrading of the surface of the item as the cylinder ismoved in the same direction as the abrading direction of the cylinderover a maximum of the surface, i.e. in the first and the third movementand at the same time can be taken to or close to the edges of the itemwithout risking the above-discussed damages to the abrasive lamellae orthe edges of the item. The third movement is in principle similar to thefirst movement and is preferably followed by a translation of thecylinder and a movement similar to the second movement etc. until thefull surface of the item has been abraded.

The translating of the cylinder is in one embodiment a translation of adistance substantially equal to a width of the cylinder, so that theoverlap between neighbouring strokes or movements is negligible orsmall, such as 1 to 3 centimetres. Alternatively, the translation isabout half the width of the cylinder so that each part of the surface isabraded twice by the cylinder.

It is preferred that the cylinder is lifted form contact with saidsurface prior to the rotation of the cylinder half a turn and thereafteris moved towards the surface for continued abrading of the surface.

The control means are in a preferred embodiment adapted to abrade asurface of an item by means of said abrading cylinder to approximate apredefined curved shape of said surface, in particular a curved shapecomprising a plurality of double curved areas, such as a wind turbineblade. Thereby, the abrasion arrangement may be employed to produceitems of a highly uniform shape, which is very difficult otherwise forlarge items such as wind turbine blades.

The abrasive means comprise preferably an elastic support element,preferably support brushes, which support the backside of the abrasivelamellae, said support element substantially having almost the samelength as the lamellae.

It is an advantage that the actual shape of the surface of the item isdetected so that the deviation between an ideal shape of the surface ofthe item may be determined and/or the deflection of the item due to thegravitational force may be determined. Thus, it is an advantage that theabrasion arrangement comprises a set of sensors for providing an inputto the control means in order for the control means to determine theactual shape of the surface of the item. Preferably, at least some ofthe set of sensors are arranged on the robotic arm. The set of sensorscomprises advantageously contactless distance sensors, in particularoptical sensors.

The abrasion arrangement comprises preferably means for correlating thedetermined actual shape of the surface of the item with datarepresenting a predefined curved shape of the finished surface of theitem to identify deviations between said ideal surface shape and theactual shape of the surface of the item. Said deviations may compriseangular displacement deviations of the item to be abraded, deformitiesin the surface of the item to be abraded and/or deflections of saidblade to be abraded when the blade is arranged to be abraded by saidabrasion arrangement.

The present invention also relates to the method of use of an abrasionarrangement as described herein for abrading the surface of wind turbineblades. Hereby, uniform wind turbine blades may be produced which isvery advantageous as the control of the wind turbine becomes more simpleand predictable when the aerodynamic properties of the individual bladesof the wind turbine are substantially identical.

BRIEF DESCRIPTION OF FIGURES

Embodiments of the present invention are illustrated in the encloseddrawing of which

FIG. 1 shows a robotic arm equipped with an abrading cylinder,

FIG. 2 is an example of an abrading cylinder within a shielding housing,

FIG. 3 is a working pattern for abrading of the surface of an elongateditem,

FIG. 4 shows a first view of the use for abrading a wind turbine blades,and

FIG. 5 shows a second view of the use for abrading a wind turbine blade.

DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION

An abrasion arrangement of the present invention for abrading of asurface 1 is shown in FIG. 1 comprising a 6-axis articulated robotic arm2 on which is mounted an abrasion head 3 having an abrading cylinder 4enclosed in a shielding housing 5 provided with a suction outlet (notshown) for removal of dust and a motor (not shown) for driving therotation of the abrading cylinder 4. The base 6 of the robotic arm 2 isin FIG. 1 mounted on a vertical column 7 equipped with parallel,vertical tracks 8 on which the base 6 is displaceable arranged in thevertical direction so as to enable abrasion of a surface 1 of a widerextent in the vertical direction than the robotic arm 2 itself allowsfor.

The abrading cylinder 4 shown in FIG. 2 has abrasive means whichcomprise abrasive lamellae 9 of an abrasive sheet, such as abrasivecloth, of which the front side 10 has abrasive properties and whichextend substantially radially from an elongated core 11 of the cylinder.The abrasive lamellae 9 are supported on the back side 9 by an elasticsupport element comprising support brushes 12 having almost the samelength as the lamellae 9. The cylinder 4 is during operation of theabrasion arrangement rotated so that the front side 10 of the abrasivelamellae 9 is moved across the surface 1 to be abraded, the direction ofrotation are indicated by the curved arrows R on FIG. 2. The tangentialmovement of the front side 10 of the lamellae 9 over the surface 1 to beabraded due to the rotation of the cylinder 4 defines the abradingdirection of the cylinder 4 indicated with straight arrow AD. The core11 of the cylinder 4 shown in FIG. 2 is equipped with helical or spiralshaped undercut grooves for retaining the flexible sanding stripsholding the abrasive lamellae 9 as well as the brushes 12 but thegrooves may in another embodiment of the present invention be straightalong the longitudinal direction of the core 11.

In a particular embodiment of the present invention, the control meansfor controlling the operation of the abrasion arrangement are adapted tolet the abrading cylinder operated according to the working patternillustrated in FIG. 3 for abrading the surface 1 of an elongated item 13having a first edge 14 and a second edge 15 both extending generally inthe longitudinal direction of the elongated item 13, such as a windturbine blade. The first edge 14 and the second edge 15 are notnecessarily parallel to each other but are substantially so as depictedin FIG. 3. The part of the working pattern described in details hereinstart at the letter “S” on FIG. 3. The abrading cylinder 4 is inabrading engagement with the surface 1 of the elongated item 13 startingat a position at the first edge 14 and moving towards the second edge 15at a first velocity and where the cylinder 4 is oriented so that theabrading direction is against the direction of movement of the abrasionhead 3, indicated with the straight arrows M in FIG. 3. The reason tohave the direction of movement M to be opposite the abrading directionAD of the cylinder 4 is that it is in that way avoided that the abrasivelamellae 9 collide with the first edge 14 which have a damaging andlife-shortening effect on the lamellae 9 as well a damaging effect onthe edge 14 of the item. However, when the direction of movement M isopposite the abrading direction AD, the abrading action on the surface 1is less efficient and the speed of the movement of the abrasion head 3must be reduced to obtain a satisfactory finish of the surface 1, forwhich reason the extent of these parts of the working pattern, generallyreferred to with the letter “B” in FIG. 3 has been minimised. When theabrasion head 3 has been moved away from the first edge 14, the abrasionhead 3 is lifted away from the item 13 so that the cylinder 4 disengagesthe surface 1 of the item 13 and the abrasion head 3 is turned around atthe position indicated in FIG. 3 with the letters “TU” so that theabrading direction AD of the cylinder 4 is reversed. Now, the abrasionhead 3 is lowered towards the item 13 until the cylinder 4 engages thesurface 1 with a sufficient force and the movement of the abrasion head3 across the surface 1 of the item towards the second edge 15 iscontinued. In this part of the working pattern, generally referred towith the letter “A” in FIG. 3, the direction of movement M and theabrading direction AD of the cylinder 4 is the same direction, theabrading action is therefore more efficient and the speed of themovement of the abrasion head 3 can be considerably higher than in the Bparts of the working pattern. When the second edge 15 is reached by theabrasion head 3, the head is translated substantially one width of thecylinder 4 in the longitudinal direction of the elongated item 13, thetranslation being indicated generally by the arrows in FIG. 3 referredto with the letters “TL”. The sequence of working patterns is nowrepeated starting from the second edge 15 and moving towards the firstedge 14 of the elongated item 13, where a part B of the working patternwhere the direction of movement M is opposite the abrading direction ADends with a turning TU of the abrasion head and is continued with a partA where the direction of movement M is the same as the abradingdirection AD, etc.

In FIG. 3 the parts A, B of the working pattern are depicted with aminor distance in between for the sake of clarity. However, the parts A,B are in the present embodiment abutting or are overlapping e.g. 1 to 3centimetres so that the whole of the surface 1 is abraded by thecylinder 4. In an alternative embodiment, the parts A, B are overlappingin the longitudinal direction of the item 13 with half the width of thecylinder 4 so that each area of the surface will be abraded twice by thecylinder 4. The areas around the edges 14, 15 may only be partly abradedby the cylinder 4 and require a manually controlled abrasion to obtainthe correct finish.

A particular embodiment and use of the present invention is shown inFIGS. 4 and 5, where two robotic arms 2, 2′ each carrying an abrasionhead 3 are mounted on each their vertical column 7, 7′ which areconnected by a horizontal crossbar 16 and supported on wheels so as tobe displaceable along an elongated item 13 on a set of tracks 17 laidout horizontally on the floor. This arrangement is particularly suitablefor abrading the surface of a wind turbine blade 13 where the two sidesbetween the leading edge 14 and the trailing edge 15 of the blade 13 canbe abraded simultaneously by the abrasion heads 3 carried by the roboticarms 3, 3′. The arrangement is displaced along the blade on the tracks17 so that the whole surface of the blade may be abraded. In order tofacilitate a compensation for the twist of the blade 13 along itslongitudinal axis 18, the blade 13 is supported so that it may berotated around its axis 18 for the blade 13 to be substantiallyhorizontally oriented at the position of the vertical columns 7, 7′.

The control system controlling the operation of the arrangement shown inFIGS. 4 and 5 comprises a predefined set of data defining the idealthree-dimensional shape of the finished blade 13 and the control systemis adapted for controlling by means of the robotic arms 2, 2′ theposition of the abrasion heads 3, the force with which they are pressedtowards the surface 1 of the blade 13 and the speed with which they aremoved across the surface 1 so as to process the surface 1 of the blade13 to approximate the predefined ideal shape of the blade 13. A set ofsensors (not shown) are arranged on the robotic arms 2, 2′ and/or on thevertical columns 7, 7′, in particular contactless distance sensors usinglaser light or ultrasonic means for providing an input to the controlsystem in order for the control system to determine the actual shape ofthe blade 13.

When e.g. a wind turbine blade 13 has been manufactured to a statebefore being abraded by the abrasion arrangement, it most likely willdeviate from the ideal blade shape/geometry of a finished blade. Suchdeviations may e.g. originate from angular displacements of the bladecompared to ideal angular displacements of the blade.

Preferred ideal wind turbine blade profiles comprise an ideal angulardisplacement to obtain an improved aerodynamic blade profile. However,the manufacturing process of the blade may result in blades that deviatefrom such ideal angular displacements.

Also, the manufacturing process of the blade may result in deformitiessuch as deformities in the surface of the blade which causes the bladeto deviate from the ideal blade shape/geometry.

Likewise, the blade may be arranged in a plurality of ways to be abradedby the abrasion arrangement. Preferably, arranging the blade comprisesthat the root end of the blade is attached to a suitable fixationarrangement (not illustrated in any figures) so the blade extendssubstantially horizontally to be abraded by the abrasion arrangement asillustrated in FIG. 5 while only being supported at the root end of theblade 13. As another example the blade may be supported by one or moresupportive structures arranged underneath the blade in the longitudinaldirection of the blade. It is however naturally understood that anysuitable way of arranging the blade so it can be abraded by the abrasionarrangement may be utilized, and furthermore e.g. a combination offixating the root end to a suitable fixation arrangement may be combinedwith supporting the blade, e.g. underneath the blade at furtherlocations along the blade.

Thus, when the blade 13 is arranged in the abrasion arrangement, it mayresult in the blade deflecting from its ideal shape due to e.g. gravity.For example, if the blade is arranged in the abrasion arrangement by theroot being attached to a fixation arrangement, the tip end/free end ofthe blade will deflect downwards. In general, the deflection of theblade is dependent of among others, the elasticity of the blade, thesize of the blade, the orientation of the blade (e.g. orientation of theleading and trailing edges of the blade) and others. Also, the blade 13may deflect in different ways dependent on the blade orientation whene.g. rotating the blade around the longitudinal direction of the bladeas illustrated in FIG. 5.

It is preferred that the abrasion arrangement facilitates taking suchangular displacement deviations, such deviations due to bladedeformities, and/or blade deflections into consideration during theabrasion process. That is, the blade 13 is preferably abraded to reduceor even remove angular displacement deviations and/or blade deformitiescompared to the ideal blade shape whereas deflections of the blade arepreferably compensated for during the abrasion so that the blade is noterroneously abraded.

Thus, it is preferred that the abrasion arrangement comprises adeviation handling arrangement for automatically handling and/orcompensating for deviations such as the above mentioned angulardisplacement deviation, the mentioned deformity deviations anddeflections due to the arrangement of the blade to be abraded.

Such a deviation handling arrangement is described in more details inFIG. 6. The deviation handling arrangement gathers information from atleast two data sources 21, 23.

The first data source 21 comprises predefined data regarding thepredefined ideal three-dimensional surface shape of the finished item,in particular a wind turbine blade as described above. This ideal itemsurface shape data may e.g. be provided by data from three-dimensionalblade drawings such as for example three-dimensional CAD drawings, froma look up table and/or any suitable other data which in self or oncombination with other data facilitates determining the ideal bladeshape/geometry.

The second data source comprises an item surface shape determinationarrangement gathering measurement data regarding the actualshape/geometry of the surface of the item to be abraded. The surfaceshape determination arrangement 23 preferably comprises an opticalarrangement, e.g. arranged at the vertical column(s) 7 and/or crossbar16, and the optical arrangement facilitates scanning the surface of theblade to detect the actual shape/geometry of the item surface. However,it is understood that the said shape determination arrangement 23 may bearranged at any appropriate location at the abrasion arrangement andthat it may comprise any suitable number of optical scanners andpossible accompanying scanner controllers.

The optical arrangement preferably comprises one or more emitters foremitting electromagnetic radiation towards the surface of the item, e.g.a wind turbine blade 13, to be abraded. This radiation is reflected fromthe surface and a part of the reflected radiation is detected by theoptical arrangement, converted into electrical signals representing thedetected reflected radiation from the surface, and these electricsignals may thus be processed by the surface shape determinationarrangement to establish information regarding the actual geometry/shapeof the item to be abraded.

In a preferred embodiment, the item surface shape determinationarrangement 23 facilitates establishing data of the actual surface shapeby establishing three-dimensional data of the surface.

The ideal surface shape data from the first data source 21 and the datafrom the surface shape determination arrangement representing thedetected actual shape/geometry of the surface is accessed/transmitted20, 22 to and correlated by data processing means 19 receiving the data.The data processing means 19 can thus, based on the said correlation,generate control signals 24 to the control means of the abrasionarrangement. Based on such control signals, the control means cancontrol the operation of the robotic arm by e.g. controlling theposition of the abrading cylinder on the surface of the item, the forcewith which the abrading cylinder is pressed towards said surface and/orthe velocity with which the abrading cylinder is moved with respect tothe surface, and hereby reduce/remove e.g. the said angular displacementdeviations and surface deformities identified by the correlation toapproximate the predefined ideal three-dimensional shape of the finisheditem. Also, the control signals preferably facilitates that the abrasionarrangement takes into consideration the deflection of the item to beabraded so the abrasion arrangement compensates for such deflectionsduring the abrasion of the surface of the item 13.

In an aspect of the invention, the deviation handling arrangementfacilitates continuously scanning the surface during abrasion of theitem surface to establish information of the surface area of the itembeing abraded and/or to establish information of the surface area of theitem to be subsequently abraded.

In another embodiment, the deviation handling arrangement may beforestarting the abrasion of the surface establish a substantially completeabrasion template for the control means to follow during abrasion of theitem by scanning the surface prior to performing the abrasion of theitem.

In a further embodiment, the deviation handling arrangement may bearranged to facilitate that scanning the surface of the item andperforming the abrasion of the item is performed during the samemovement of the vertical column(s) 7 along the item to be abraded. Thus,the data from the optical arrangement is continuously processed andcorrelated with the ideal item surface shape data to continuouslygenerate an output for the control means during the movement along theitem to be abraded.

1.-18. (canceled)
 19. An abrasion arrangement to abrade a surface of anitem, the arrangement comprising a multiple-axis robotic arm having atleast five axes, an abrading cylinder mounted on the robotic arm andcomprising abrasive means which comprise abrasive lamellae of anabrasive sheet, such as abrasive cloth, of which the front side hasabrasive properties and which extend substantially radially from anelongated core and means for driving said core to rotate around alongitudinal axis of the core, and control means for controlling theoperation of the robotic arm so as to control e.g. the position of theabrading cylinder on said surface, the force with which the abradingcylinder is pressed towards said surface and the velocity with which theabrading cylinder is moved with respect to said surface, wherein thecontrol means are adapted to move the abrading cylinder across saidsurface to alternate between first movement in a direction substantiallyperpendicularly to the longitudinal axis of the core and substantiallyin the same direction as an abrading direction of the rotated cylinder,the first movement being continued until an edge of said surface isreached, translating the cylinder substantially in a directionperpendicularly to the direction of the first movement, second movementin a direction substantially perpendicularly to the longitudinal axis ofthe core and substantially against an abrading direction of the rotatedcylinder, rotation of the cylinder half a turn to reverse the abradingdirection thereof with respect to said surface, and third movement in adirection substantially perpendicularly to the longitudinal axis of thecore and substantially in the same direction as an abrading direction ofthe rotated cylinder.
 20. An abrasion arrangement according to claim 19,wherein said translating of the cylinder is a distance substantiallyequal to a width of the cylinder.
 21. An abrasion arrangement accordingto claim 19, wherein the cylinder is lifted from contact with saidsurface prior to the rotation of the cylinder half a turn.
 22. Anabrasion arrangement according to claim 19, wherein the control meansare adapted to abrade a surface of an item by means of said abradingcylinder to approximate a predefined curved shape of said surface. 23.An abrasion arrangement according to claim 22, wherein said predefinedcurved shape comprises a plurality of double curved areas.
 24. Anabrasion arrangement according to claim 19, wherein the abrasive meanscomprise an elastic support element, preferably support brushes, whichsupport the backside of the abrasive lamellae, said support elementsubstantially having almost the same length as the lamellae.
 25. Anabrasion arrangement according to claim 19, wherein said robotic armcomprises six axes.
 26. An abrasion arrangement according to claim 19,wherein said item is a wind turbine blade.
 27. An abrasion arrangementaccording to claim 19, comprising a set of sensors for providing aninput to the control means in order for the control means to determinethe actual shape of the surface of the item.
 28. An abrasion arrangementaccording to claim 27, wherein at least some of the set of sensors arearranged on the robotic arm.
 29. An abrasion arrangement according toclaim 27, wherein the set of sensors comprises contactless distancesensors, in particular optical sensors.
 30. An abrasion arrangementaccording to claim 27, wherein said abrasion arrangement comprises meansfor correlating the determined actual shape of the surface of the itemwith data representing a predefined curved shape of the finished surfaceof the item to identify deviations between said ideal surface shape andthe actual shape of the surface of the item.
 31. An abrasion arrangementaccording to claim 30, wherein said deviations comprise angulardisplacement deviations of the item to be abraded.
 32. An abrasionarrangement according to claim 30, wherein said deviations comprisedeformities in the surface of the item to be abraded.
 33. An abrasionarrangement according to claim 30, wherein said deviations comprisedeflections of said item to be abraded when the item is arranged to beabraded by said abrasion arrangement.
 34. An abrasion arrangementaccording to claim 19, wherein the arrangement is configured forabrading the surface of wind turbine blades.